Surface-mounted cartridge fuses generally comprise a hollow, insulating body defining a fuse element-receiving passageway opening onto the opposite outer ends thereof. One and preferably all sides of the body have a flat surface parallel to the longitudinal axis of the fuse so that the fuse will not roll when placed on a printed circuit board. Cup-shaped metal end caps are telescoped over the opposite ends of the insulating fuse body. In a surface mounted fuse, it is also sometimes desirable that the end caps have a consistent square profile larger than the fuse body and presenting identical flat surfaces also extending parallel to the fuse axis so that any side of the end cap can lay flush against a conductive area on a printed circuit board. The end caps are leadless and the sides of the end caps are generally soldered to these spaced conductive areas on the surface of the printed circuit board.
The fuse elements of miniature cartridge surface-mounted fuses commonly comprise fuse wires extending diagonally across the fuse bodies where they are bent back over the body ends and sandwiched between the end caps and the fuse body.
Surface-mounted fuses are commonly applied to the printed circuit boards by automated equipment which grasps the individual fuses and applies them to the desired areas of the printed circuit board where the end caps thereof are to be soldered thereto. The reliability of the application procedure by automated fuse grasping and carrying equipment is facilitated if the exposed portion of the fuse body has a square rather than a round shape. By making the fuse symmetrical, the fuse grasping procedure is simplified since it is a simple matter to grasp any flat side of a fuse and then properly position it on the board so that corresponding parallel flat sides of the end caps rest upon the flat conductive areas of the printed circuit board. One example of such a surface mounted fuse is disclosed in U.S. Pat. No. 4,920,327, granted Apr. 24, 1990. The fuse body disclosed therein has a consistent square cross section throughout its length and square sided end caps which close and envelope the open, square ends of the fuse body.
Miniature surface-mounted fuses pose particularly difficult assembly problems in their fabrication. In the first place, the fuse wires are very thin and so can be readily severed if during assembly of the end caps to the fuse body the fuse wire bent back ends are crushed and/or stretched to a breaking point. As disclosed in the latter patent, in an effort to avoid stretching the fuse wire during assembly of the end cap to the fuse body ends recesses are formed in the outer periphery of the fuse body to receive the bent back portions of the fuse wire. However, the solder coated end walls of the end caps press against the portion of the fuse wire extending over the outer faces of the fuse body and so can crush and damage the fuse wire. The assembly procedures for such a fuse also requires a precise positioning of the fuse wire so the ends thereof fit into the recesses.
The present invention provides a rectangular-sided, surface-mounted fuse having a substantially different and improved construction from that disclosed in U.S. Pat. No. 4,920,327. This unique construction avoids damage to the fine fuse wire without the need for recesses in the periphery of the fuse body, and without the need for compressing the ends of the fuse wire between the end caps and the end faces of the fuse body.